Conventional hybrid vehicles are powered by an engine and one or more electric motor/generators, which in turn may be powered or energized by a rechargeable battery. In a charge-depleting mode, the battery is slowly allowed to discharge or drop to a threshold minimum charge level over the course of travel, and may be recharged, for example, by using available energy from the engine output, the motor/generator, and/or by plugging the battery into an available energy source, such as an electrical outlet, when the vehicle reaches its destination.
During hybrid vehicle operation, a control method typically selects a preferred power source or combination of power sources (i.e. the engine and/or one or more motor/generators) in order to power the hybrid vehicle in an optimally fuel efficient manner. The control method also monitors battery charge level and schedules battery recharging in order to ensure the motor/generators remain operational to drive the hybrid vehicle. The battery is maintained in a charge-deleting or charge-sustaining mode. In general, a battery enters a charge-depleting mode when a control method selects the motor/generator as the preferred power source, such as while the vehicle is accelerating from a standstill, and draws energy from the battery, thereby depleting the battery charge. In a charge-sustaining mode, the battery is maintained at a particular charge level, preserving or sustaining the battery charge level.
The efficiency of a given control method or algorithm in managing the selection and/or combination of available hybrid power sources is affected by various external factors. For example, the distance of a vehicle trip or route, route topography, and the frequency of braking over the course of the route, each influence the vehicle speed profile over that route. The ability to “look ahead” at a planned route in determining an optimal powertrain strategy may therefore help maximize fuel economy of the hybrid vehicle over the route.